JP2542783B2 - Method and apparatus for forming powder as a powder layer - Google Patents

Abstract

A method and apparatus (10) for selectively sintering a layer of powder to produce a part comprising a plurality of sintered layers. The apparatus includes a computer (40) controlling a laser (12) to direct the laser energy onto the powder to produce a sintered mass. The computer either determines or is programmed with the boundaries of the desired cross-sectional regions of the part. For each cross-section, the aim of the laser beam is scanned over a layer of powder and the beam is switched on to sinter only the powder within the boundaries of the cross-section. Powder is applied and successive layers sintered until a completed part is formed. The powder may consist of a plastic, metal, ceramic, or polymer substance. In the preferred embodiment, the aim of the laser is directed in a continuous raster scan and the laser turned on when the beam is aimed within the boundaries of the particular cross-section being formed. Preferably, the powder dispensing mechanism includes a drum which is moved horizontally across the target area and counter-rotated to smooth and distribute the powder in an even layer across the target area. A downdraft system provides controlled temperature air flow through the target area to moderate powder temperature during sintering. <IMAGE>

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method and apparatus for dispensing powder as a powder bed.

The method and apparatus, in particular, sequentially form powder layers and direct a directed energy beam, eg, a laser beam, at selected locations in the powder layers to selectively sinter to form the desired components in a stack. It is particularly useful for dispensing and forming powder layers in manufacturing computer assisted laser devices.

[0003]

When attempting to form a flat powder layer on the underlying surface, it is often the case to use a leveling member to achieve a uniform thickness. However, when flattening using a leveling member, undesired disturbance of the powder often occurs, and shear force acts on the powder, so that a material that is easily deformed or deteriorated is used as the powder layer. If the proper result was not obtained. In particular, in the case of powders of polymers such as nylon, aggregation and sticking easily occur due to heat, and in such cases, agglomeration often occurs due to the action of stress, and agglomerated parts are formed in a flattened layer. However, when the thickness is thin, recesses may be formed due to the lack thereof, and there are many problems in the homogeneity of the powder layer.

In particular, the powder layer is sequentially formed, the energy beam is directed to the selected position to selectively sinter and fuse, and this operation is repeated to produce a desired part. In the directed energy beam sintering method,
Such problems must be solved by all means.

[0005]

Most of the problems mentioned above are
It is solved by the method and device of the present invention. In the present invention, when the powder is dispensed onto the target area to form a flat powder layer, for example, a certain amount of powder is supplied at one end of the area and the required thickness of the powder layer is obtained from the end. The drum is moved along the target area from the one end to the other end while keeping a certain distance, and the drum is operated so as to leave a flat layer after passing through the drum.
It is characterized by rotating in the (outer) direction, that is, performing counter rotation. The drum moves along the target area while being counter-rotated and comes into contact with the pile of powder on the front surface to expel the powder in said direction of movement, leaving behind the drum a powder layer with a desired spacing thickness .

The method and apparatus for dispensing the powder of the present invention to form a powder layer is, in particular, to selectively sinter selected portions of the powder layer to be successively formed by a directed energy beam such as a laser beam. It is suitable for a method of producing desired parts in a laminated manner. Equipment for such selective sintering includes a laser or other directional energy source that selectively emits a beam to a target area where the component is manufactured. A powder dispensing system deposits powder on the target area.
A laser control mechanism moves the target of the laser beam and also modulates the laser to sinter the powder layer spread on the target area. The control mechanism selectively sinters only the powder within the limited boundaries to produce the desired layer of the part. A control mechanism causes a laser to selectively sinter the powder layers sequentially to form an overall part made up of layers that are sintered together. The boundaries of each sintering zone correspond to a respective cross-sectional area of the part. Preferably, the control mechanism is a computer, such as CAD / C, for identifying boundaries for each layer.
Including AM system. That is, the computer, given the data of the overall size and shape of the part, specifies the boundary for each layer and operates the laser control mechanism corresponding to the specified boundary. Alternatively, the specific boundaries of each layer can be programmed into the computer from scratch.

That is, in the selective sintering method, a step of depositing a first portion of powder on a target surface and a step of scanning a target of a directed energy beam (preferably a laser beam) along the target surface, Sintering the first layer of the first powder portion on the target surface. The first layer is the first of the portions
Corresponds to the section area. Sintering the powder by scanning the directional energy source when the laser beam target is within the boundary defining the first layer. A second portion of the powder is deposited on the first sintered layer and a laser beam target is scanned along the surface of the first sintered layer. Sintering the second layer by scanning the directional energy source when the target of the laser beam is inside the boundary of the second layer of the second powder portion. The sintering of the second layer simultaneously joins the first and second layers to form a cohesive mass as a unit. The powder portions are sequentially deposited on the previously sintered layers and each deposited layer is sequentially sintered. In one embodiment, the powder is continuously deposited in the target area.

The laser beam is modulated on and off during the raster scan so that the powder is sintered when the target of the laser beam is directed inside the boundaries of the respective layers. Preferably the laser beam is controlled by a computer. The computer includes a CAD / CAM system which provides the computer with data regarding the overall size and shape of the part to be manufactured, which computer defines the boundaries of each target area of the part. The computer uses the determined boundaries to control the sintering of each layer corresponding to the cross-sectional area of the part. In another embodiment, the computer is programmed with only boundary data for each cross sectional area of the part.

In the selective and directed energy beam sintering method, it is preferable to provide a downward air feeding mechanism for adjusting the powder temperature. The mechanism includes a support defining a target area, a mechanism for delivering air to the target area, and a mechanism for controlling the air temperature before reaching the target area. The support is
It includes a porous medium for depositing the powder and a plenum adjacent to the medium. In this way, temperature-controlled air is delivered to the powder in the target area, promoting temperature control of the sintered and non-sintered powder in the target area.

The drawings illustrate a selective directed energy beam sintering process. FIG. 1 shows an exploded perspective view of the entire apparatus by the same method. Overall, the device 10 is a laser 1
2, powder dispenser 14, and laser control means 16. More specifically, the powder dispenser 14 has a hopper 20 for receiving the powder 22, the hopper having an outlet 24. The outlet 24 is oriented to dispense the powder into a target area 26, which area 26 is generally defined in FIG. Of course, many other embodiments are possible for dispensing the powder 22.

The components of the laser 12 are shown somewhat schematically in FIG. 1, which includes a laser head 30, a safety shutter 32 and a front mirror assembly 34. The type of laser used depends on many factors, especially the type of powder 22 to be sintered. In the embodiment of FIG. 1, an Nd: YAG laser (laser metrics 95
00Q) was used. It has a maximum output of 100 watts in continuous mode and can operate in continuous mode or pulsed mode. The laser beam output of the laser 12 is
It has a wavelength of about 1060 nM, which is close to infrared light. The laser 12 illustrated in FIG. 1 includes an internal pulse rate generator having a selected range of about 1 kilohertz to 40 kilohertz and a duration of about 6 nanoseconds. In either pulsed mode or continuous mode, the laser 12 can be on-off modulated to selectively generate a laser beam traveling along the path indicated by the arrows in FIG.

To focus the laser beam, focusing lenses 36 and 38 are placed along the path of the laser beam as shown in FIG. Only by using the focusing lens 38, the position of the true focal point cannot be easily adjusted by changing the distance between the focusing lens 38 and the laser 12. The focusing lens 36 arranged between the laser 12 and the focusing lens 38 creates an imaginary focal point between the focusing lens 36 and the laser 12. By varying the distance between the focusing lens 38 and the imaginary focus, the true focus can be controlled along the laser beam path of the focusing lens 38 on the side opposite to the laser 12. In recent years, many advances have been made in the optics field, and there are many other ways to efficiently focus a laser beam at a fixed location.

More specifically, the laser control means 16 includes a computer 40 and a scanning system 42. In the preferred embodiment, computer 40 includes a laser control microprocessor and a CAD / CAM system for data generation. In the embodiment illustrated in FIG. 1, a personal computer is used (Commodore 64), the main attributes of which include an accessible interface port and a flag line which generates a non-maskable interrupt.

As shown in FIG. 1, the scanning system 42 includes a prism 44 that redirects the path of the laser beam. Of course, the specific layout of the apparatus 10 is a fundamental factor in determining whether a single prism or multiple prisms 44 are required for steering the laser beam path. Further, the scanning system 42 is a galvanometer 48,
It includes a pair of reflectors 46, 47 driven by 49. The galvanometers 48 and 49 are the reflecting mirrors 46 and 47, respectively.
Are connected to respective reflecting mirrors so as to selectively orient. The galvanometers 48, 49 are mounted at right angles to each other and therefore the reflectors 46, 47 are mounted at right angles to each other.
The function generating driver 50 controls the movement of the galvanometer 48 (the galvanometer 49 is subordinate to the movement of the galvanometer 48),
Therefore the target of the laser beam (indicated by the arrow in FIG. 1)
Are controlled in the target area 26. As shown in FIG. 1, the driver 50 is operably connected to the computer 40. Other scanning methods can be used for use as the scanning system 42, such as acousto-optic scanners, rotating polygon mirrors, and resonant mirror scanners.

FIG. 2 is a perspective view showing a raster pattern of a laser beam with respect to a part of an article manufactured by the same method and a target area. In FIG. 2, a portion of component 52 is shown schematically, which consists of four layers 54-57. The target of the laser beam 64 is a raster scan pattern 66. In this specification, "target" is a directional neutral term and does not mean the modulation state of the laser 12. For convenience, axis 68 is the fast scan axis and axis 70 is the slow scan axis. The axis 72 is the forming direction of the part.

6 and 7 show an embodiment of the powder dispenser 20 in the selective laser beam sintering method. Overall, the support 100 defines a target area 102 against which the target of the laser beam 64 is directed (FIG. 1). The hopper 104 dispenses the powder 106 through the opening 108 into the target area 102. A metering roller (not shown) is placed in the opening 108 and when this roller is rotated,
A quantity of powder is linearly arranged at the end 110 of the target area 102.

A leveling mechanism 114 spreads the powder pile 106 toward the other end 112 of the target area. Leveling mechanism 114
Is an outer knurled surface
e) with a cylindrical drum 116. A motor 118 mounted on the bar 120 drives the pulley 122 and the belt 1
It is connected to the drum 116 via 24 and rotates it.

The leveling mechanism 114 also includes a mechanism 126 for moving the drum 116 between one end 110 and the other end 112 of the target area. The mechanism 126 includes an X / Y table 128 that moves the bar 120 horizontally and vertically. That is, the table 128 is fixed, and the plate 130 is selectively movable with respect to the table 128.

FIG. 8 shows a device for controlling the temperature of the product being manufactured.
Shown in Due to the difference between the temperature of the particles not yet scanned by the laser beam and the temperature of the particles already scanned,
It has been observed that undesirable shrinkage of the product during manufacture occurs. It has been discovered that the downflow of temperature controlled air through the target area can adjust for such undesirable temperature differences. Temperature-controlled downward air supply device 1 shown in FIG.
32 reduces such shrinkage by heat exchange between the upper layer of powder particles to be sintered and air. This heat exchange regulates the temperature of the upper layer of the particles to be sintered, controls the average temperature of the upper layer, and removes volumetric heat from the manufactured product to prevent the product from growing into a non-sintered material. . The temperature of the inflowing air is not lower than the softening point of the powder, but is adjusted to be not higher than the temperature at which sufficient sintering occurs.

The lower air delivery device 132 includes a support 134 defining a target area 136, means for directing air toward the target area, a mechanism for controlling the temperature of the incoming air such as an electrical resistance 142, and the like. Means for delivering air to the target area include a chamber 138 surrounding the support 134 and an air delivery fan 14.
0 and / or suction fan 141. Window 144
Introduces the target of beam 64 (FIG. 1) to target area 136. A powder dispensing mechanism (not shown) as shown in FIG. 1 or FIG. 7 is located at least partially within the chamber 138 to dispense the powder onto the target area 136.

The support 134 is a honeycomb-shaped porous medium 14.
8 supports the filter medium 146 (pore paper). A plenum 150 is arranged to collect and direct air to the outlet 152. Of course, outlet 152 is connected to vacuum source 141 or other air treatment mechanism.

The basic idea of this method consists in forming the parts layer by layer. That is, the part is considered to consist of a plurality of separate cross-sectional areas, which are stacked to form the three-dimensional structure of the part. Each cross-sectional area is defined by a two-dimensional boundary, and of course each area can have its own unique boundary. Further, preferably, the thickness of each layer (dimension in the direction of the axis 72) is constant.

In this method, a first portion of powder 22 is placed in target area 26 and selectively sintered by laser beam 64 to produce first sintered layer 54 (FIG. 2). This first sintering area 54 corresponds to the first cross-sectional area of the desired part. The laser beam selectively sinters the disposed powder 22 only within the defined boundaries.

Of course, there are other methods of selectively sintering the powder 22. One way is to direct the target of the laser beam in a "vector" fashion. That is, the beam actually follows the contour and interior of each cross-sectional area of the desired portion. Alternatively, the target of the beam 64 is manipulated in a repetitive pattern and the laser 12 is modulated. In FIG. 2, a raster manipulation pattern 66 is used, which is superior to the vector system because of its simplicity of implementation. Another method consists in combining the vector method and the raster operation method, tracing the desired boundary of one layer in the vector method and illuminating the inside of the boundary in the raster operation mode. Of course, there is a choice as to which method to choose. For example, in raster mode, the axes 68, 7 of the raster pattern 66 are compared to vector mode.
The disadvantage is that it only approximates arcs and lines that are not parallel to 0. In some cases, the resolution of the part is reduced when manufactured in raster pattern mode. However, raster mode is superior to vector mode because of its simplicity of implementation.

Returning to FIG. 1, the target area 26 is scanned with a laser beam 64 target in a continuous raster pattern.
The driver 50 controls the galvanometers 48, 49 to produce the raster pattern 66 (FIG. 2). The movement of the reflector 46 controls the movement of the laser beam 64 target along the fast scan axis 68 (FIG. 2), while the movement of the reflector 47 targets the laser beam 64 along the slow scan axis 70. Control the movement of.

Computer 40 holds information about the cross-sectional area of the next part to be made. Therefore, a portion of the loose powder 22 is dispensed into the target area 26 and the target of the laser beam 64 is moved in its continuous raster pattern. Computer 40 modulates laser 12 to selectively generate a laser beam in raster pattern 66 at desired intervals. In this way, the directed beam of the laser 12 selectively sinters the powder 22 in the target area 26 to obtain the desired sintered layer with the desired cross-sectional area boundaries. This process is repeated layer by layer, sintering the layers together to form an agglomerated part, such as part 52 of FIG.
To manufacture.

Due to the relatively low power output of the laser head 30 shown in FIG. 1, the powder 22 comprises a low heat of fusion plastic material (eg ABS) compatible with this low power output.
Several types of post-forming treatments are conceivable for the parts produced by the apparatus 10 of the present invention. For example, if the part produced in this way is used as a prototype model, that is, a mold for sand casting or wax casting, no post-forming treatment is necessary. In other cases, some post-forming is performed to design some of the manufactured parts to tight tolerances. Alternatively, certain types of parts need to have certain material properties, which may be performed by heat treatment and / or chemical treatment of the part. For example, the particle size of the powder 22 can be set to produce parts with open porosity, and if a substance such as epoxy is injected into the part, the desired injection characteristics, such as compressive strength, wear resistance, etc. can be achieved. The characteristics, homogeneity, etc. are obtained.

A few properties have been identified which improve the performance of powder 22. First, the absorption energy of the powder can be controlled by adding a pigment such as carbon black. By adjusting the concentration and composition of the additive, the absorption rate k of the powder
Can be controlled. Generally, the energy absorption rate is governed by the following exponential decay relation. I (z) = Io exp (kZ) where I (z) is the optimum absorbed energy intensity in the powder at a perpendicular distance z to the surface (powder per unit area),
Io is the surface value of I (energy intensity on the surface), and k is the absorptance. By adjusting the absorptance k and adjusting the thickness of the layer that absorbs a certain amount of beam energy, the energy absorbed during this step can be controlled entirely.

Another important property of the powder is the aspect ratio of the particles (ie the ratio of the maximum size to the minimum size of the particles). That is, particles having a range of aspect ratios tend to bend during the shrinking of the part. For particles with a low aspect ratio, i.e. almost spherical particles,
The shrinkage of the part becomes more three-dimensional, resulting in greater curvature. When using particles with a high aspect ratio (eg, flakes or rods), shrinkage occurs primarily in the vertical direction, reducing or eliminating the curvature of the part. High aspect ratio particles are believed to have greater bonding degrees of freedom, with interparticle contacts preferentially oriented in the horizontal plane and shrinkage predominantly in the vertical direction.

[0030]

EXAMPLE FIGS. 6 and 7 show an example of an apparatus for dispensing and forming the powder of the present invention as a powder layer. It has been found that the dispensing mechanism 114 forms a controlled flat powder layer in the target area 102 without disturbing the parts being manufactured. A weighed amount of powder 106 is deposited at the end 110 of the target area 102. When the powder is dispensed, the drum 116 is moved to the end 11
Move from 0. After the powder is dispensed in a pile, as shown in FIG. 7, the plate 130 and bar 120 (and associated mechanism) are raised vertically. The plate 130 moves toward the hopper 104 to bring the drum 116 into position adjacent the pile of powder along the end 110. There, the drum 116 is lowered into contact with the powder peaks and moved horizontally along the target area 102 to spread the powder peaks into a flat layer. Of course, since it is possible to control the exact position of the plate 130 with respect to the table 128,
The distance between the drum 116 and the target area 102 can be precisely controlled to give the powder layer the desired thickness. Preferably, the spacing between the drum 116 and the target area 102 is constant, resulting in a parallel movement, although other spacing options are possible.

A motor 118 causes the drum 116 to rotate in reverse as the drum 116 is moved horizontally along the target area 102 from the distal end 110 to the other end 112. As shown in FIG. 6, "reverse rotation (computer-rota)
“Tion)” means that the drum 116 is rotated in the opposite direction R with respect to the direction M of horizontal movement along the target area 102.

More specifically, the drum 11 in FIG.
6 contacts the rear end 160 of the powder pile 106 and is rotated in reverse at high speed. The mechanical action of the drum on the powder ejects the powder in the direction of movement M, so that the ejected particles fall into the tip area 162 of the powder pile. A smooth flat powder layer 164 is left behind the drum 116 (between the drum 116 and the end 110) as shown in FIG.

FIG. 6 also shows that the powder 106 can be distributed over the target area without disturbing the previously sintered powder 166 or the unsintered powder 168. That is, the drum 116 is moved along the target area without shearing the previously formed layer or disturbing the product being manufactured. Since there is no such shearing action, the sintered particles 166 and the non-sintered particles 168 are
A smooth powder layer 106 can be distributed over the fragile base layer in the target area including and.

[0034]

As is apparent from FIG. 6, according to the present invention, since the drum rotates in the reverse direction, the drum comes into contact with the rear end 160 of the powder ridge 106 on the front surface to remove the powder at the contact portion. It is blown off and dropped onto the tip portion 162 of the powder pile. Thus, in the present invention, only the particles that come into contact with the front surface of the drum are lifted upward, and are skipped and ejected at the tip of the mountain. Only the powder that comes into contact with the drum moves, and the other powders are not affected. In particular, there is no effect on the already formed flat powder layer 164. Therefore, no shearing force is applied to the formed flat surface. No problem occurs even if the powder is easily altered or deformed.

In the case of the selective laser sintering method, a polymer such as nylon is often used, but in such a case, aggregation and sticking are likely to occur. When a force such as a shearing force acts here, the particles agglomerate and adversely affect the flat layer, but such defects are avoided in the present invention.

In addition to the above, it will be apparent that the present invention exerts an excellent effect even when the base body has a fragile surface.

The selective laser sintering method allows relatively complicated parts to be manufactured relatively easily. Those skilled in the art will appreciate that the components shown in FIG. 3 are difficult to manufacture by conventional machining methods. It is difficult, if not impossible, to manufacture cavities 82 and posts 84 by machine tools, especially if the parts are of relatively small dimensions. The present invention is extremely useful in enabling such a manufacturing method.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of an apparatus used for a selective and directed energy beam sintering method,

FIG. 2 is a perspective view showing a laser beam raster pattern for a part and a target area of a component manufactured by a selective directed energy beam sintering method;

FIG. 3 is a perspective view showing an example of a component manufactured by a selective and directed energy beam sintering method,

4 is a partial cross-sectional view of the component of FIG. 3,

5 is a cross-sectional view taken along line 7-7 of FIG. 3,

FIG. 6 is a schematic vertical cross-sectional view of an apparatus for dispensing powder of the present invention,

FIG. 7 is an explanatory perspective view of the powder dispensing apparatus of the present invention,

FIG. 8 is a schematic explanatory view of a powder temperature adjusting device in a selective directed energy beam sintering method.

Front Page Continuation (72) Inventor Deckard, Carl Earl, Texas, USA, Austin, Lake, Austin, Boulevard, You, Tee, M, Etch, Pee, Number, 94 (56) References -21906 (JP, A)

Claims (16)

(57) [Claims] 1. Dispensing a pile of powder at one end of an area,
In a device for forming a powder layer in this area, a drum means and a predetermined distance between the area and the drum,
Means for moving the drum from one end to the other end of the zone, and means for rotating the drum in a direction opposite to the direction of movement of the drum from one end to the other end of the zone, the drum being rotated in reverse When moving from the one end to the other end, it contacts the pile of powder to expel the powder in the direction of movement, and has approximately the desired spacing thickness between the drum means and the one end. A powder layer forming device configured to leave a powder layer. 2. The desired spacing is constant.
An apparatus according to claim 1. 3. An apparatus according to claim 1, wherein said area is flat, said desired spacing is constant and said drum means is adapted to move parallel to said area. 4. The apparatus of claim 1 wherein said drum means is a cylinder having a substantially uniform circular cross section. 5. The device of claim 4, wherein the cylinder has a knurled outer surface. 6. The apparatus of claim 1, including means for depositing the powder pile proximate the one end. 7. A method of forming a powder layer on an area of a surface, comprising: supplying a quantity of powder at a location proximate to the area; and crossing the area from a position prior to the location of the quantity of powder. Moving the drum; rotating the drum in a direction opposite to the direction of movement of the drum across the zone; and transferring a quantity of powder to the counter rotating drum during movement of the drum across the zone. A method of forming a powder layer, comprising the steps of contacting to leave a powder layer on the area after the moving step. 8. The method of claim 7, wherein the drum is maintained at a desired distance from the zone during the moving step. 9. The method of claim 8, wherein the desired spacing is a constant distance from the zone and the zone is flat. 10. The method of claim 7, wherein the surface of the drum has a rough texture. 11. The method of claim 7, wherein the surface of the drum is knurled. 12. The method of claim 7, wherein said feeding step comprises depositing a powder pile at a location proximate said area. 13. The method of claim 7, wherein the powder is capable of being sintered. 14. The method of claim 13, wherein the area of the surface containing the powder has a portion in a sintered state and a portion in a non-sintered state. 15. The method of claim 7, wherein in the contacting and moving step, powder is ejected in the direction of movement as a result of contact between the drum and the powder. 16. The method of claim 7, wherein said feeding step comprises feeding a metered amount of powder at said location proximate said area.